The technique of providing a plurality of antennas both on the transmitting side and on the receiving side, preparing a plurality of radio wave channels in space between the radio transmitting side and the radio receiving side and transmitting space-multiplexed signals through channels is known as “MIMO”, and it is possible to improve transmission efficiency according to MIMO.
There is a link adaptation technique as a peripheral technique of MIMO. Link adaptation refers to a technique of adaptively controlling the M-ary modulation number (transmission rate), coding rate and transmission power distribution, according to changes in the channel environment between the transmitting side and the receiving side.
When link adaptation is applied to MIMO, it is possible to effectively utilize MIMO channels by distributing power to streams (transmitting antennas and beams for which data is assigned). Further, in a good quality environment, it is possible to realize high frequency use efficiency using M-ary modulation such as 16 QAM and 64 QAM.
On the other hand, generally, a common pilot is transmitted at a constant power all the time by applying link adaptation or taking into account monitoring with respect to other cell for handover.
The wireless communication apparatus disclosed in Patent Document 1 is known using such a technique. This communication apparatus will be briefly described On the receiving side, transmission power assigned for the streams is estimated based on channel estimation values and estimated transmission power is reported to the transmitting side using feedback signals. On the transmitting side, transmission power is assigned based on the feedback signals. Here, channel capacity can be maximized by setting (power distribution) transmission power according to the propagation condition of each stream.    Patent Document 1: Japanese Patent Application Laid-Open No. 2003-078461